Fuel cell power generation system

Abstract

To shorten a downtime while suppressing fatigue and progress of deterioration of a cell stack due to the rapid temperature drop during shutdown.SOLUTION: A fuel cell power generation system includes a fuel cell unit 6 that includes a cell stack 6B formed by stacking a plurality of solid oxide fuel cells 6A that generate electricity through an electrochemical reaction between a reformed fuel gas obtained by reforming a fuel gas in a reforming portion 4 and an oxidizing gas, and outputs the electromotive force of the cell stack 6B as generated power, an operation control unit 9A capable of executing an operation stop process that lowers the temperature of the fuel cell unit 6 to a target temperature and stops operation, and temperature drop rate adjusting means B that can freely adjust the temperature drop rate of the fuel cell unit 6, and the operation control unit 9A monitors the temperature drop rate of the fuel cell unit 6 during execution of the operation stop process, and executes stop time temperature control of controlling the temperature drop rate adjusting means B such that the temperature drop rate becomes a predetermined set drop rate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell power generation system having a cell stack made up of multiple stacked solid oxide fuel cell cells that generate electricity through an electrochemical reaction between reformed fuel gas obtained by reforming fuel gas in a reforming section and an oxidant gas, and is equipped with a fuel cell section that outputs the electromotive force of the fuel cell cells as generated power to an electric power grid. [Background technology]

[0002] In this type of fuel cell power generation system, the fuel cell section operates at a high temperature during power generation operation, and when operation is stopped, a shutdown process is performed to reduce the amount of reformed fuel gas supplied to the fuel cell section while cooling the fuel cell section, thereby lowering the fuel cell section from a high temperature to a target temperature such as room temperature. Patent Document 1 describes a fuel cell power generation system that, during shutdown processing, stops the supply of reformed fuel gas to the anode and flows steam through the anode, in order to avoid damage caused by the difference in thermal stress between the anode and cathode of the fuel cell due to cooling, and monitors the temperature difference between the anode and cathode while flowing air through the cathode of the fuel cell section, and controls the amount of steam supplied to the anode and the amount of air supplied to the cathode so that the temperature difference falls within a certain range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5521467 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if the temperature difference between the anode and cathode is kept within a certain range during shutdown processing, if the cell stack suddenly drops from a high temperature to the target temperature in a short period of time, large thermal stress will be generated in the cell stack, and there is a concern that the repeated and accumulated large thermal stress will cause fatigue and deterioration of the cell stack. Therefore, it is possible to consider cooling the cell stack slowly over time to prevent fatigue and deterioration, but in that case, the shutdown time until the temperature of the cell stack drops to the target temperature would be extended, which could result in a time delay before restarting, resulting in a period when power generation is not possible, or could increase the amount of fuel gas consumed during the shutdown process.

[0005] In view of this situation, the main object of the present invention is to provide a fuel cell power generation system that can reduce the downtime while suppressing the progression of fatigue and deterioration of the cell stack due to a sudden drop in temperature when operation is stopped. [Means for solving the problem]

[0006] The first characteristic configuration of the present invention is a fuel cell unit having a cell stack formed by stacking a plurality of solid oxide fuel cell units that generate electric power by an electrochemical reaction between an oxidant gas and a reformed fuel gas obtained by reforming a fuel gas in a reforming unit, and that outputs the electromotive force of the cell stack as generated electric power; an operation control unit capable of executing an operation stop process to stop operation by lowering the temperature of the fuel cell unit to a target temperature; a temperature drop rate adjusting means for adjusting the temperature drop rate of the fuel cell section; The operation control unit monitors the temperature drop rate of the fuel cell unit during the operation shutdown process, and performs shutdown temperature control by controlling the temperature drop rate adjustment means so that the temperature drop rate becomes a predetermined set drop rate.

[0007] According to this configuration, shutdown temperature control is performed while the fuel cell unit is being shut down, and while monitoring the actual rate of temperature drop in the fuel cell unit, the rate of temperature drop can be adjusted to a predetermined set rate that takes into account the fatigue and deterioration of the cell stack and the shutdown time.This makes it possible to reduce the shutdown time while suppressing the progression of fatigue and deterioration of the cell stack due to a sudden drop in temperature when the unit is shut down. Furthermore, this shutdown temperature control does not cause the temperature drop rate adjustment means to perform a preset operation, but rather causes the means to perform an operation according to the actual temperature drop rate when the fuel cell unit is stopped.Therefore, regardless of variations in the operating temperature and ambient temperature of each fuel cell power generation system, the temperature drop rate when the fuel cell unit is stopped can be adjusted to a predetermined set drop rate, thereby achieving the above-mentioned effects.

[0008] A second characteristic configuration of the present invention is provided with a status information acquisition unit that acquires status information relating to a deterioration state or an aged usage state of the cell stack, The operation control unit corrects the set descent speed in accordance with the state information acquired by the state information acquisition unit.

[0009] Depending on the state of the cell stack, such as its state of deterioration or its state of long-term use, it is possible that fatigue and degradation of the cell stack due to temperature changes may be more likely to progress. According to this configuration, the state information acquisition unit acquires state information, such as the state of deterioration or state of long-term use of the cell stack, and the operation control unit corrects the set lowering rate in accordance with the state information. For example, if the state is such that fatigue and degradation of the cell stack due to temperature changes are more likely to progress, the set lowering rate can be corrected to a slower rate when operation is stopped, so that fatigue and degradation of the cell stack are less likely to progress. Therefore, the progression of fatigue and degradation of the cell stack due to temperature drops when operation is stopped can be appropriately suppressed in accordance with the state of the cell stack, such as its state of deterioration or state of long-term use.

[0010] In a third characteristic configuration of the present invention, the state information acquisition unit acquires a temperature or a power generation voltage of the cell stack during operation as state information relating to a deterioration state of the fuel cell unit, The operation control unit corrects the set lowering speed in accordance with the temperature or power generation voltage of the cell stack during operation acquired by the state information acquisition unit.

[0011] As the deterioration of the cell stack progresses, phenomena occur such as the temperature of the cell stack during operation becoming higher than the initial temperature, or the generated voltage of the cell stack during operation becoming lower than the initial voltage. With this configuration, the state information acquisition unit acquires the temperature or generated voltage of the cell stack during operation as state information related to the deteriorated state of the cell stack, and the operation control unit corrects the set drop rate accordingly, so that information related to the deteriorated state of the cell stack can be easily acquired and the progression of fatigue and deterioration of the cell stack due to temperature drop when operation is stopped can be appropriately suppressed according to the deteriorated state of the cell stack.

[0012] In a fourth characteristic configuration of the present invention, the state information acquisition unit acquires a cumulative number of starts and stops or a cumulative operating time of the cell stack as state information relating to the aging usage state of the fuel cell unit, The operation control unit corrects the set descending speed in accordance with the cumulative number of starts and stops or cumulative operating time of the cell stack acquired by the state information acquisition unit.

[0013] When the cumulative number of starts and stops or cumulative operating time of the cell stack increases, it is expected that the cell stack is deteriorating due to long-term use. With this configuration, the status information acquisition unit acquires the cumulative number of starts and stops or cumulative operating time of the cell stack as status information related to the long-term usage state of the cell stack, and the operation control unit corrects the set descent rate accordingly, so that information related to the long-term usage state of the cell stack can be easily acquired and the progression of fatigue and degradation of the cell stack due to temperature drops when operation is stopped can be appropriately suppressed according to the long-term usage state of the cell stack.

[0014] A fifth characteristic configuration of the present invention is that the operation control unit monitors the temperature drop rates at multiple locations in the fuel cell unit while the operation shutdown process is being executed, and controls the temperature drop rate adjustment means so that the temperature drop rate at the location with the fastest temperature drop rate becomes the set drop rate.

[0015] According to this configuration, when controlling the rate of temperature drop when operation is stopped, the rate of temperature drop at the location with the fastest rate of temperature drop among multiple locations in the fuel cell section is controlled, which provides safer control and more reliably suppresses the progression of fatigue and deterioration of the cell stack due to temperature drop when operation is stopped.

[0016] A sixth characteristic configuration of the present invention is that the set temperature drop rate is set to be different depending on the temperature range so that the temperature drop rate in the temperature range where the thermal stress generated in the cell stack due to temperature change is large is lower than the temperature drop rate in the temperature range where the thermal stress generated in the cell stack due to temperature change is small.

[0017] According to this configuration, when operation is stopped, the rate of temperature drop in the temperature range where the thermal stress generated in the cell stack due to temperature change is large is set lower than the rate of temperature drop in the temperature range where the thermal stress generated in the cell stack due to temperature change is small, thereby efficiently suppressing the progression of fatigue and deterioration of the cell stack due to temperature drop when operation is stopped and shortening the operation stop time.

[0018] A seventh characteristic configuration of the present invention is an air supply passage for supplying air containing the oxidant gas to the fuel cell portion; an air supply amount adjusting means for adjusting the flow rate of air supplied to the fuel cell unit through the air supply path; The temperature drop rate adjusting means is configured as the air supply amount adjusting means, and by adjusting the flow rate of air supplied to the fuel cell section through the air supply path, the temperature drop rate of the fuel cell section can be freely adjusted by the cooling effect of the air.

[0019] According to this configuration, the temperature drop rate adjusting means can be configured efficiently by utilizing the air supply passage for supplying the air containing the oxidant gas to the fuel cell section and the air supply amount adjusting means. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a fuel cell power generation system. [Figure 2] Image of the control map for the set descent speed (graph) DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuel cell power generation system according to an embodiment of the present invention will be described with reference to the accompanying drawings. As shown in Figure 1, this fuel cell power generation system is equipped with a desulfurization unit 1 that desulfurizes hydrocarbon fuel gas such as city gas, a vaporization unit 3 that heats reforming water supplied from a reforming water tank 2 to generate steam, a reforming unit 4 that uses the steam generated in the vaporization unit 3 to steam reform the fuel gas desulfurized in the desulfurization unit 1, and a fuel cell unit 6 that generates power using the reformed fuel gas obtained in the reforming unit 4 and oxidant gas (oxygen gas) in the air supplied from a blower 5 (an example of an air supply amount adjustment means).

[0022] This fuel cell power generation system also includes a combustion section 7 that mixes the exhaust reformed fuel gas discharged from the fuel cell section 6 after the power generation reaction with exhaust air and burns the combustible components in the exhaust reformed fuel gas, a power conversion section 8 that converts the power generation output of the fuel cell section 6 to the same voltage and frequency as the power received from the commercial power source 17, and a control device 9 that controls the operating state of each section.

[0023] This fuel cell power generation system is configured such that the vaporization section 3, reforming section 4, fuel cell section 6, and combustion section 7 are housed within a storage container 10, and the vaporization section 3 performs a process of generating steam using the combustion heat generated by combustion in the combustion section 7, while the reforming section 4 performs a process of reforming fuel gas using the combustion heat generated by combustion in the combustion section 7.

[0024] Fuel gas is supplied to the desulfurization unit 1 through a fuel gas supply path L1 by operation of a boost pump 11 (an example of a fuel gas supply amount adjusting means). Reforming water in the reforming water tank 2 is supplied to the vaporization unit 3 through a reforming water supply path L2 by operation of a reforming water pump 12 (an example of a reforming water supply amount adjusting means). A downstream portion of the fuel gas supply path L1 from the desulfurization unit 1 merges with a midpoint of the reforming water supply path L2, and the reforming water and fuel gas merged outside the storage container 10 are supplied to the vaporization unit 3 provided inside the storage container 10. The fuel gas containing water vapor produced in the vaporization unit 3 is supplied through a water vapor-containing fuel gas supply path L3 to the reforming unit 4, where the fuel gas is steam reformed to produce a reformed fuel gas mainly composed of hydrogen gas. The reformed fuel gas produced in the reforming unit 4 is supplied to the fuel cell unit 6 through a reformed fuel gas supply path L4.

[0025] The fuel cell section 6 has a cell stack 6B made up of a plurality of stacked solid oxide fuel cell cells 6A that generate electricity through an electrochemical reaction between the reformed fuel gas and the oxidant gas, and is configured to output the electromotive force of the cell stack 6B as generated power. The plurality of fuel cell cells 6A are provided in the cell stack 6B in a state where they are electrically connected in series.

[0026] The fuel cell 6A is provided with a fuel conduit 6a through which the reformed fuel gas flows and an air conduit 6b through which the air flows, and although not shown, a solid electrolyte layer is provided between the fuel electrode and the air electrode, and the reformed fuel gas flows through the fuel conduit 6a to supply the reformed fuel gas to the fuel electrode, and the air flows through the air conduit 6b to supply the air to the air electrode. The cell stack 6B is arranged in the storage container 10 with multiple fuel cell cells 6A arranged in an orientation such that the reformed fuel gas outlet of the fuel conduit 6a and the air outlet of the air conduit 6b face upward.

[0027] 1, the fuel cell section 6 is provided with a gas manifold 6C that receives reformed fuel gas supplied from the reforming section 4 through the reformed fuel gas supply path L4, and the multiple fuel cell units 6A are arranged above the gas manifold 6C, with the gas manifold 6C connected to gas inlets at the lower ends of the fuel flow sections 6a of the multiple fuel cell units 6A. The reformed fuel gas supplied to the gas manifold 6C is supplied to the fuel flow sections 6a of each of the multiple fuel cell units 6A from the gas inlets at the lower ends, flows through each fuel flow section 6a from bottom to top, and is used in the power generation reaction, and the waste reformed fuel gas after being used in the power generation reaction is discharged from the reformed fuel gas discharge port at the top end.

[0028] The storage container 10 is provided with an air inlet 13, and an air supply path L5 is connected to the air inlet 13. By operating a blower 5 (an example of an air supply amount adjusting means), air is supplied into the storage container 10 through the air supply path L5. An air supply hole (not shown) that connects the inside of the storage container 10 to the inside of the air flow section 6b is provided near the lower end of the air flow section 6b in each of the plurality of fuel cell cells 6A. Air from inside the storage container 10 is supplied to the air flow section 6b of each of the plurality of fuel cell cells 6A through this air supply hole, flows through each air flow section 6b from the bottom to the top, and is used for the power generation reaction, and the exhaust air after being used for the power generation reaction is discharged from the air outlet at the top end.

[0029] Within the storage container 10, the space between the cell stack 6B, which is made up of a plurality of stacked fuel cells 6A, and the reforming section 4 arranged above the cell stack 6B, is configured as a combustion section 7 that combusts the exhaust reformed fuel gas and exhaust air discharged from the upper ends of the fuel cells 6A. The combustion heat generated by the combustion of combustible components in the exhaust reformed fuel gas in the combustion section 7 is used to generate steam in the vaporization section 3, and is used for the reforming process in the reforming section 4.

[0030] The storage container 10 has an exhaust section 14 formed on the bottom surface or the like, which exhausts the combustion gas generated in the combustion section 7 to the outside. The storage container 10 is provided with a combustion catalyst section 15 (e.g., a platinum-based catalyst) which removes carbon monoxide gas from the combustion exhaust gas exhausted to the outside from the exhaust section 14.

[0031] The power conversion unit 8 is an inverter or the like electrically connected to the cell stack 6B, and can convert the power output of the cell stack 6B into power of a desired voltage, frequency, and phase and output it. Then, power is supplied to a power load device (not shown) via a power supply line L6 connected to the power conversion unit 8. The power supply line L6 is connected to a commercial power source 17, and power is supplied to the power load device from at least one of the commercial power source 17 and the cell stack 6B.

[0032] The control device 9 is equipped with an operation control unit 9A that controls the operation of the fuel cell power generation system. The operation control unit 9A controls the operation of each unit, such as the boost pump 11, the blower 5, the reforming water pump 12, and the power conversion unit 8, and adjusts the amount of fuel gas and reforming water supplied to the vaporization unit 3, the amount of air supplied into the storage container 10, and the amount of combustion in the combustion unit 7, and executes various processes, such as a startup process in which the temperature of the fuel cell unit 6 is raised to a power generation temperature (T0 in FIG. 2) to start up the fuel cell unit 6 at a high temperature, an operation process in which the fuel cell unit 6 generates electricity in the high-temperature state after the startup process, and an operation stop process in which the temperature of the fuel cell unit 6 is lowered from the high-temperature state to a target temperature (see T1 in FIG. 2) close to room temperature to stop operation.

[0033] During the startup process, the amount of fuel gas and reforming water supplied to the vaporization section 3, the amount of air supplied into the storage container 10, the amount of combustion in the combustion section 7, etc. are gradually increased to set amounts, thereby raising the temperature of the fuel cell section 6 to the desired power generation temperature and bringing it to a high-temperature state for startup. In the operation process, for example, the amount of fuel gas and reforming water supplied to the vaporization section 3, the amount of air supplied into the storage container 10, the amount of combustion in the combustion section 7, etc. are sequentially adjusted according to the power load measured by the power load measuring section 16 provided on the power supply line L6, thereby causing the fuel cell section 6 in a high-temperature state to output generated power according to the power load. During the operation shutdown process, the amount of fuel gas and reforming water supplied to the vaporization section 3, the amount of air supplied into the storage container 10, the amount of combustion in the combustion section 7, etc. are gradually reduced, and the temperature of the fuel cell section 6, which is in a high temperature state, is lowered to the target temperature, thereby stopping operation.

[0034] Here, if the cell stack 6B of the fuel cell unit 6 suddenly drops from a high temperature to the target temperature in a short time during the operation shutdown process, a large thermal stress will be generated in the cell stack 6B, and there is a concern that the repetition and accumulation of this large thermal stress will accelerate fatigue and deterioration of the cell stack 6B. On the other hand, if the cell stack 6B is cooled slowly over time to prevent fatigue and deterioration, there is a concern that the operation shutdown time will be extended.

[0035] Therefore, in order to reduce the duration of shutdown while suppressing the progression of fatigue and deterioration of the cell stack 6B due to a sudden drop in temperature when the operation is stopped, the operation control unit 9A is configured to monitor the actual temperature drop rate of the fuel cell unit 6 during the execution of the operation shutdown process, and to perform shutdown temperature control by controlling the temperature drop rate adjustment means B so that the temperature drop rate becomes a predetermined set drop rate (see Figure 2).

[0036] In this embodiment, multiple temperature sensors 18 (an example of a temperature measurement means) are provided to measure the temperatures at different locations in the cell stack 6B, and during shutdown temperature control, the operation control unit 9A monitors the temperature drop rates at multiple locations in the cell stack 6B, and sets the temperature drop rate at the location with the fastest temperature drop rate as the temperature drop rate to be controlled, and controls the temperature drop rate adjustment means B so that this temperature drop rate becomes the set drop rate.

[0037] In this embodiment, the temperature drop rate adjusting means B is implemented by a blower 5, and is configured to adjust the flow rate of air supplied to the fuel cell unit 6 through the air supply path L5, thereby freely adjusting the temperature drop rate of the fuel cell unit 6 through the cooling effect of the air. The operation control unit 9A controls the operation of the blower 5 so that the flow rate of air supplied to the fuel cell unit 6 through the air supply path L5 is the sum of the air flow rate required for the operation shutdown process and the air flow rate required for adjusting the temperature drop rate. Incidentally, the temperature of the air supplied to the fuel cell unit 6 through the air supply path L5 is the ambient temperature of the fuel cell power generation system. Therefore, when adjusting the temperature drop rate from the high power generation temperature to the low target temperature, a small flow rate is sufficient in the high temperature range where there is a large difference from the ambient temperature, but the flow rate increases as the temperature drops and approaches the ambient temperature.

[0038] During the operation shutdown process, the operation control unit 9A sequentially acquires and monitors the temperature drop rate of the controlled object of the cell stack 6B, and if the temperature drop rate at that time is faster than the set drop rate, it controls the operation of the blower 5 to decrease the flow rate of air supplied to the fuel cell unit 6, and if the temperature drop rate at that time is slower than the set drop rate, it controls the operation of the blower 5 to increase the flow rate of air supplied to the fuel cell unit 6, thereby adjusting the temperature drop rate of the cell stack 6B to the set drop rate using a feedback method.

[0039] Each of (a) to (d) in Figure 2 is an image (graph) of a control map for the set descent rate. The horizontal axis represents elapsed time, the vertical axis represents temperature, and the temperature descent rate is expressed as a gradient. The solid line in the graph indicates the preset set descent rate, and the dashed-dotted line in the graph indicates the corrected set descent rate, as will be described in detail later.

[0040] As shown in Figure 2, the set temperature drop rate is set to a different rate depending on the temperature range.For example, as shown in multiple patterns in (a) to (d) of Figure 2, the temperature drop rate in a temperature range where the thermal stress generated in the cell stack 6B due to temperature change is large is set to be slower than the temperature drop rate in a temperature range where the thermal stress generated in the cell stack 6B due to temperature change is small.

[0041] Figures 2(a) and 2(b) show examples of set drop rates that are used when the temperature range where the thermal stress generated in the cell stack 6B due to temperature changes is large is in the high temperature range on the power generation temperature T0 side, and the temperature drop rate in the high temperature range on the power generation temperature T0 side is set to be slower than the temperature drop rate in the low temperature range on the target temperature T2 side. In the control map shown in Figure 2(a), the temperature drop rate in the temperature range from the high-side power generation temperature T0 to the intermediate temperature T1 between the power generation temperature T0 and the target temperature T2 is set to a first set value, and the temperature drop rate in the low-side temperature range from the intermediate temperature T1 to the target temperature T2 is set to a second set value that is larger than the first set value. In addition, the control map shown in FIG. 2(b) is set so that the temperature drop rate gradually increases from the high temperature side to the low temperature side.

[0042] Figures 2(c) and 2(d) show examples of set drop rates that are used when the temperature range where the thermal stress generated in the cell stack 6B due to temperature change is large is in the low temperature range on the target temperature T2 side, and the temperature drop rate in the low temperature range on the target temperature T2 side is set to be slower than the temperature drop rate in the high temperature range on the power generation temperature T0 side. In the control map shown in Figure 2(c), the temperature drop rate in the temperature range from the high-side power generation temperature T0 to the intermediate temperature T1 between the power generation temperature T0 and the target temperature T2 is set to a third set value, and the temperature drop rate in the low-side temperature range from the intermediate temperature T1 to the target temperature T2 is set to a fourth set value that is smaller than the third set value. In addition, the control map shown in FIG. 2(d) is set so that the temperature drop rate gradually slows down from the high temperature side to the low temperature side.

[0043] Depending on the state of deterioration of the cell stack 6B, it is possible that fatigue and deterioration of the cell stack 6B due to temperature changes may be more likely to progress. Therefore, in this fuel cell power generation system, a status information acquisition unit 9B is provided that acquires status information regarding the deterioration state of the cell stack 6B so that the progression of fatigue and deterioration of the cell stack 6B due to temperature drop when operation is stopped can be appropriately suppressed even when fatigue and deterioration of the cell stack 6B is likely to progress due to temperature change, and the operation control unit 9A is configured to execute a correction process to correct the set descent rate when the status information regarding the deterioration state of the cell stack 6B acquired by the status information acquisition unit 9B satisfies the correction condition.

[0044] As the deterioration of the cell stack 6B progresses, phenomena such as the temperature of the cell stack 6B during operation becoming higher than the initial temperature and the power generation voltage of the cell stack 6B during operation becoming lower than the initial voltage occur. Therefore, in this embodiment, the status information regarding the deterioration state of the cell stack 6B is the temperature and generated voltage (an example of temperature or generated voltage) of the cell stack 6B during operation, and the status information acquisition unit 9B sequentially acquires the temperature measured by the temperature sensor 18 and the generated voltage measured by the power conversion unit 8, etc. Furthermore, the correction condition for correcting the set lowering speed is that at least one of the following conditions is satisfied: a first condition that the temperature of the cell stack 6B is higher than the initial temperature, and a second condition that the power generation voltage of the cell stack 6B is lower than the initial voltage. Alternatively, the correction condition can be that both the first and second conditions are satisfied.

[0045] In the above-mentioned correction process, the operation control unit 9A determines whether the temperature and power generation voltage of the cell stack 6B during operation acquired by the status information acquisition unit 9B satisfy the above-mentioned correction conditions, and if the correction conditions are satisfied, corrects the preset set descent speed (solid line portion in the graph of Figure 2) to a lower speed (dotted line portion in the graph of Figure 2).

[0046] Figure 2 shows an example in which both the temperature drop rate in the temperature range where the thermal stress generated in the cell stack 6B due to temperature change is large (slower temperature drop rate) and the temperature drop rate in the temperature range where the thermal stress generated in the cell stack 6B due to temperature change is small (faster temperature drop rate) are corrected to a slower rate, but it is also possible to correct either one of them to a slower rate, for example, by correcting only the temperature drop rate in the temperature range where the thermal stress generated in the cell stack 6B due to temperature change is small (faster temperature drop rate).

[0047] In this way, when the temperature and power generation voltage of the cell stack 6B during operation satisfy the correction conditions, the set drop rate is corrected to a slower rate, and the temperature drop rate when operation is stopped is made slower so that fatigue and deterioration of the cell stack 6B are less likely to progress.This makes it possible to appropriately suppress the progression of fatigue and deterioration of the cell stack 6B due to temperature drop when operation is stopped, even when fatigue and deterioration of the cell stack 6B are more likely to progress due to temperature changes. The state information relating to the deterioration state of the cell stack 6B may be either the temperature or the power generation voltage of the cell stack 6B during operation.

[0048] [Another embodiment] Other embodiments of the present invention will be described below. Note that the configurations of the embodiments described below are not limited to being applied independently, but can also be applied in combination with the configurations of other embodiments.

[0049] (1) In the above-described embodiment, an example was shown in which a unit for acquiring state information related to the degradation state of the cell stack 6B was provided, and the operation control unit 9A executed a correction process to correct the set descent speed in accordance with the state information related to the degradation state of the cell stack 6B acquired by the state information acquisition unit 9B. Alternatively, a unit for acquiring state information related to the aging state of the cell stack 6B may be provided, and the operation control unit 9A may execute a correction process to correct the set descent speed in accordance with the state information related to the aging state of the cell stack 6B acquired by the state information acquisition unit 9B.

[0050] When the cumulative number of starts and stops of the cell stack 6B or the cumulative number of starts and stops or cumulative operating time of the cell stack 6B increases, it is expected that deterioration of the cell stack 6B is progressing due to long-term use. Therefore, in this embodiment, the status information regarding the deterioration state of the cell stack 6B is the cumulative number of starts and stops and the cumulative operating time of the cell stack 6B, and the status information acquisition unit 9B monitors the operating state of the fuel cell unit 6, counts the cumulative number of starts and stops of the cell stack 6B, and measures the cumulative operating time of the cell stack 6B. Furthermore, the correction condition for correcting the set descending speed is that at least one of the following conditions is satisfied: a third condition that the cumulative number of starts and stops of the cell stack 6B is greater than the set number, and a fourth condition that the cumulative operating time of the cell stack 6B is greater than the set operating time. Alternatively, the correction condition can be that both the third and fourth conditions are satisfied.

[0051] In the above-mentioned correction process, the operation control unit 9A determines whether the cumulative number of starts and stops and cumulative operating time of the cell stack 6B acquired by the status information acquisition unit 9B satisfy the above-mentioned correction conditions, and if the correction conditions are satisfied, corrects the preset set descent speed (solid line portion in the graph of Figure 2) to a lower speed (dotted line portion in the graph of Figure 2).

[0052] In this way, when the cumulative number of starts and stops and cumulative operating time of the cell stack 6B satisfy the correction conditions, the set drop rate is corrected to a slower rate to make the temperature drop rate when operation is stopped slower so that fatigue and deterioration of the cell stack 6B are less likely to progress. This makes it possible to appropriately suppress the progression of fatigue and deterioration of the cell stack 6B due to temperature drop when operation is stopped, even when fatigue and deterioration of the cell stack 6B are more likely to progress due to temperature changes. In the above embodiment, the state information relating to the state of use of the cell stack 6B over time may be either the cumulative number of starts and stops or the cumulative operating time of the cell stack 6B.

[0053] (2) In the above-described embodiment, the temperature drop rate adjusting means B is configured as a blower 5 (an example of an air supply rate adjusting means) that adjusts the flow rate of air used to operate the fuel cell section 6, and the temperature drop rate of the fuel cell section 6 can be freely adjusted by the cooling effect of the air. Alternatively, the temperature drop rate adjusting means B may be configured with a reforming water pump 12 (an example of a reforming water supply amount adjusting means) that adjusts the flow rate of reforming water for operation of the fuel cell section 6, and the temperature drop rate of the fuel cell section 6 may be freely adjusted by the cooling effect caused by evaporation of the reforming water in the vaporization section 3. Alternatively, the temperature drop rate adjusting means B may be configured with a boost pump 11 (an example of a fuel gas supply amount adjusting means) that adjusts the flow rate of fuel gas for operation of the fuel cell section 6, and the temperature drop rate of the fuel cell section 6 may be freely adjusted by adjusting the combustion amount in the combustion section 7 by adjusting the fuel gas. Furthermore, the temperature drop rate adjusting means B may be a means for supplying cooling air, water, or the like into the storage container 10, separate from the means for operating the fuel cell section 6.

[0054] (3) In the above embodiment, the operation control unit 9A, during shutdown temperature control, directly measures the temperature of the cell stack 6B using the temperature sensor 18 to monitor the rate of temperature drop in the fuel cell section 6. However, the rate of temperature drop in the fuel cell section 6 may also be monitored by indirectly estimating the temperature of the cell stack 6B using the measurement results of other temperature sensors that measure the temperature inside the storage container 10, the combustion temperature in the combustion section 7, the temperature of the reforming section 4, etc.

[0055] (4) In the above embodiment, an example was given in which the set temperature drop rate was set to a different rate depending on the temperature range, but a constant temperature drop rate may also be set regardless of the temperature range. [Explanation of symbols]

[0056] 4. Modification section 5 Blower (air supply volume adjustment means) 6 Fuel cell section 6A fuel cell 6B Cell Stack 9A Operation control unit 9B Status information acquisition unit B Temperature drop rate adjustment means L5 Air supply line T2 target temperature

Claims

1. a fuel cell section having a cell stack formed by stacking a plurality of solid oxide fuel cell units that generate electricity by an electrochemical reaction between an oxidant gas and a reformed fuel gas obtained by reforming a fuel gas in the reforming section, and that outputs the electromotive force of the cell stack as generated electricity; an operation control unit capable of executing an operation stop process to stop operation by lowering the temperature of the fuel cell unit to a target temperature; a temperature drop rate adjusting means for adjusting the temperature drop rate of the fuel cell section; the operation control unit monitors the temperature drop rate of the fuel cell unit during the operation shutdown process, and executes shutdown temperature control to control the temperature drop rate adjustment means so that the temperature drop rate becomes a predetermined set drop rate; a state information acquisition unit that acquires state information relating to a deterioration state or a state of aging of the cell stack, The operation control unit corrects the set descending speed to a lower speed in accordance with the state information acquired by the state information acquisition unit.

2. the state information acquisition unit acquires a temperature or a power generation voltage of the cell stack during operation as state information relating to a deterioration state of the fuel cell unit; 2. The fuel cell power generation system according to claim 1, wherein the operation control unit corrects the set lowering speed to a lower speed in accordance with the temperature or generated voltage of the cell stack during operation acquired by the state information acquisition unit.

3. the state information acquisition unit acquires a cumulative number of starts and stops or a cumulative operating time of the cell stack as state information relating to the aging state of the fuel cell unit; 2. The fuel cell power generation system according to claim 1, wherein the operation control unit corrects the set lowering speed to a lower speed in accordance with the cumulative number of starts and stops or cumulative operating time of the cell stack acquired by the state information acquisition unit.

4. The fuel cell power generation system according to any one of claims 1 to 3, wherein the operation control unit monitors the temperature drop rates at multiple locations in the fuel cell unit during the shutdown temperature control, and controls the temperature drop rate adjustment means so that the temperature drop rate at the location with the fastest temperature drop rate becomes the set drop rate.

5. A fuel cell power generation system as described in any one of claims 1 to 4, wherein the set temperature drop rate is set to be different depending on the temperature range so that the temperature drop rate in a temperature range where the thermal stress generated in the cell stack due to temperature change is large is slower than the temperature drop rate in a temperature range where the thermal stress generated in the cell stack due to temperature change is small.

6. an air supply channel for supplying air containing the oxidant gas to the fuel cell section; an air supply amount adjusting means for adjusting the flow rate of air supplied to the fuel cell unit through the air supply path; A fuel cell power generation system as described in any one of claims 1 to 5, wherein the temperature drop rate adjustment means is configured as the air supply amount adjustment means, and by adjusting the flow rate of air supplied to the fuel cell section through the air supply path, the temperature drop rate of the fuel cell section can be freely adjusted by the cooling effect of the air.

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